1. Field of the Invention
This invention relates to a method of determining a tool running path in an N/C (numerical control) machining system.
2. Description of the Prior Art
Recently there has been put into wide use an automatic programming system in which a computer is employed to control an NC machining system.
For example, when a pressing die having a complicate curved surface is machined, the surface of a work is directly cut using N/C data prepared from CAD (computer-aided design) data without using a plaster master or the like.
The tool for cutting a work is first positioned away from the work and is moved toward the work to be brought into contact with the work at a part to be cut. After cutting the part, the tool is removed from the work, and is moved to another part to be cut if any, and finally is returned to the original position. The path along which the tool is moved during cutting operation on each part to be cut is determined on the basis of the shape of the surface to be formed thereon using the CAD data. In this specification, the path of the tool along which the tool is to be moved during cutting operation on each part to be cut will be referred to as "cutting trajectory", and the path of the tool along which the tool is to be moved in the whole cutting operation including the path along which the tool is moved toward the work from the original position to the tool inlet end of the cutting trajectory for the first part to be cut, the path along which the tool is returned to the original position from the tool outlet end of the cutting trajectory for the last part to be cut and the paths along which the tool is moved from part to part as well as the respective cutting trajectories will be referred to as "tool running path" in order to make a distinction therebetween.
When a plurality of parts of a work are to be cut, the tool running path is determined to pass a predetermined point so that the tool does not interfere with the work when moved from one part to another as disclosed, for instance, in Japanese Patent Publication No. 1(1989)-58018.
When preparing the N/C data from the CAD data, the cutting trajectories for the parts to be cut are first calculated on the basis of the CAD data and are edited. Then the cutting order of the parts (which determines the "tool running path") and the cutting conditions for the respective parts are determined and the N/C data is obtained by combining the cutting trajectories and the cutting conditions.
Conventionally the operator determines the cutting order of the parts and the cutting conditions for the respective parts on the basis of the cutting trajectories. However, since the number of the cutting trajectories to be calculated to cut the work into a predetermined three-dimensional shape is as large as several hundreds to several thousands, it takes a long time to prepare the N/C data and it is very difficult to minimize the tool running path.